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Hurricane Oscar Forecast Discussion Number 9
2018-10-29 03:45:42| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Oct 28 2018 000 WTNT41 KNHC 290245 TCDAT1 Hurricane Oscar Discussion Number 9 NWS National Hurricane Center Miami FL AL162018 1100 PM AST Sun Oct 28 2018 Satellite imagery indicates that the structure of Oscar has changed little over the past several hours. Microwave imagery has shown a ring or eye feature which is at least partly encircled by deep convection, and an eye has made occasional appearances in infrared imagery. Satellite intensity estimates have changed little, so the initial intensity remains 65 kt. One change from the previous advisory is that recent scatterometer data show that Oscar has smaller 34-kt wind radii than previously thought, so the initial and forecast wind radii have been modified. The initial motion remains 270/14. Oscar is approaching the western end of a large low- to mid-level ridge over the central Atlantic, and thus it should turn northwestward with a decrease in forward speed during the next 24 h or so. From 24-72 h, the hurricane should recurve into the mid-latitude westerlies on the east side of a deep-layer trough moving eastward through the western and central Atlantic. The models are in good agreement on the forecast track through 72 h, then show significant differences based on whether Oscar merges with a new cut-off low pressure area over the central Atlantic or remains a separate system in the westerlies. The latest GFS has joined the UKMET in showing Oscar racing northeastward into the northeastern Atlantic by 120 h as a separate system. In contrast, the HWRF and the FV3 models show a sharp turn toward the south as the new low captures Oscar. The ECMWF is between these extremes in showing a more gradual turn toward the east well to the east of the HWRF/FV3 and well to the southwest of the GFS/UKMET. The new forecast track is a little west of the previous track in the early part of the forecast based on the current position and motion. Later in the forecast period, it has been shifted a little to the east in best agreement with the ECMWF. Oscar is forecast to remain in a moist and unstable environment for the next 36-48 h, and the trough approaching from the west is likely to create a divergent outflow pattern. Based on this, the intensity forecast now shows a faster rate of strengthening than the previous advisory. After reaching its peak intensity in 36-48 h, it appears likely that the extratropical transition will occur near the 72 h point before the winds drop below hurricane force. After transition, Oscar is expected to gradually decay. It should be noted that if the FV3 scenario verifies, Oscar may maintain tropical cyclone status beyond 72 h. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 25.6N 57.0W 65 KT 75 MPH 12H 29/1200Z 25.9N 58.3W 70 KT 80 MPH 24H 30/0000Z 27.1N 59.0W 80 KT 90 MPH 36H 30/1200Z 29.1N 58.3W 85 KT 100 MPH 48H 31/0000Z 32.0N 56.0W 85 KT 100 MPH 72H 01/0000Z 39.0N 48.5W 75 KT 85 MPH...POST-TROP/EXTRATROP 96H 02/0000Z 44.0N 38.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 03/0000Z 45.0N 29.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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Hurricane Oscar Forecast Discussion Number 8
2018-10-28 21:57:11| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Oct 28 2018 000 WTNT41 KNHC 282057 TCDAT1 Hurricane Oscar Discussion Number 8 NWS National Hurricane Center Miami FL AL162018 500 PM AST Sun Oct 28 2018 Visible and infrared satellite imagery indicate that Oscar's convective pattern has continued to improve overall today, with a small eye having developed and been briefly evident between 1700-1800Z. Satellite intensity estimates range from T4.0/65 kt (TAFB and SAB) to T4.4/75 kt (UW-CIMSS ADT). The initial intensity has been increased to 65 kt, which is just below the UW-CIMSS SATCON consensus estimate of 68 kt. Oscar is moving westward or 270/14 kt. The compact hurricane is expected to move around the southwestern and western periphery of a deep-layer ridge for the next 36 hours or so, resulting in a westward motion overnight, followed by a turn toward the west-northwest and northwest on Monday, with a slow motion toward the north expected by early Tuesday. By late Tuesday and continuing into Friday, Oscar is forecast to turn northeastward and accelerate ahead of an eastward-moving deep-layer trough that currently lies just east of the U.S. east coast. This large synoptic-scale feature is expected to keep Oscar away from the United States, the Bahamas, and Bermuda. The only fly-in-the-ointment concerning the track forecast occurs on day 5 when a strong shortwave trough is forecast to dig southward down the west side of Oscar, possibly capturing the small cyclone over the north Atlantic and forcing it southward instead of allowing the small hurricane to recurve deeper into the high-latitude westerlies. All of the global and regional models are now indicating this interaction, with the only difference being whether Oscar remains a separate tropical system or merges with the shortwave trough. For now, the new official forecast follows the trend of the previous advisory and shows Oscar remaining a separate entity, but slowing down considerably as an extratropical cyclone on days 4 and 5, which is similar to that depicted by the consensus models HCCA and TVCN. Oscar is forecast to remain within an environment of mid- to upper-level temperatures that are colder than average by 2-3 deg C due to the cyclone still being embedded within the original parent larger-scale upper-level low/trough. The combination of the below- average environmental temperatures overlying relatively warm SSTs of 26.5 deg C will result in strong instability, which will aid the generation of deep convection, especially overnight. Add in Oscar's small radius of maximum winds (RMW) of 10-15 nmi, and conditions appear to be conducive for continued strengthening. The shear directly over the inner-core region is fairly low as noted by anticyclonic cirrus outflow now apparent in visible and water vapor imagery, a condition that also favors continued strengthening for the next 48 hours or so. The HWRF, HMON, and Navy COAMPS-TC models bring Oscar to major hurricane strength by 48 hours, which isn't out of the realm of possibilities based on the small RMW and expected low vertical wind shear. However, the official intensity forecast remains on the conservative side due to expected occasional intrusions of very dry mid-level air, which could briefly interrupt the intensification process. By 72 hours and beyond, increasing southwesterly shear ahead of the aforementioned deep-layer trough is expected to induce a weakening trend, which will be enhanced by Oscar moving over sub-23 deg C SSTs shortly thereafter. The cold SSTs are expected to aid the transition to a strong extratropical cyclone. The new intensity forecast is similar to the previous advisory, except to push forward the timing of peak intensity to 48 hours, and it is a little below the HCCA and IVCN intensity consensus models due to the aforementioned dry air issues. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 25.7N 55.5W 65 KT 75 MPH 12H 29/0600Z 26.1N 57.1W 70 KT 80 MPH 24H 29/1800Z 26.9N 58.4W 75 KT 85 MPH 36H 30/0600Z 28.2N 58.5W 80 KT 90 MPH 48H 30/1800Z 30.7N 57.0W 85 KT 100 MPH 72H 31/1800Z 38.0N 50.2W 80 KT 90 MPH 96H 01/1800Z 45.0N 39.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 02/1800Z 45.0N 30.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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Tropical Storm Oscar Forecast Discussion Number 7
2018-10-28 15:50:41| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Oct 28 2018 000 WTNT41 KNHC 281450 TCDAT1 Tropical Storm Oscar Discussion Number 7 NWS National Hurricane Center Miami FL AL162018 1100 AM AST Sun Oct 28 2018 Deep convection has redeveloped near the center of Oscar since early this morning and its low-level center is no longer exposed. Satellite intensity estimates have not changed since last night and the estimated intensity of 60 kt is above the various techniques. The initial intensity estimate is based primarily on the latest available ASCAT data from last night around 0100 UTC that showed maximum winds of 55-60 kt. Given the recent increase in convection observed near the center of Oscar, it seems unlikely that the winds have decreased since that time. It is worth noting that the small inner-core of Oscar increases the uncertainty of the intensity estimate, and could make the cyclone susceptible to short term intensity fluctuations that are nearly impossible to forecast or precisely detect. Virtually no change has been made to the intensity forecast. The tropical storm is moving over sufficiently warm water to support intensification and it is located within a light to moderate shear environment. All the intensity models forecast at least some strengthening, and Oscar is expected to become a hurricane later today or tonight, with some additional strengthening possible through Wednesday. Extratropical transition is forecast to begin soon thereafter, which will likely result in a decrease in the maximum winds, even as the extent of tropical-storm-force winds rapidly increases. This process is expected to be complete by 120 h. The new NHC intensity forecast is very close to the intensity consensus IVCN at all forecast hours. Oscar turned abruptly westward earlier this morning, and the initial motion estimate is now 270/10 kt. The tropical cyclone is forecast to continue moving generally westward for another 12 to 24 h on the south side of a mid-layer ridge over the northern central Atlantic. Oscar should then turn toward the north between the ridge and a mid-latitude trough approaching from the west. By Wednesday, the cyclone is expected to accelerate north-northeastward or northeastward as it becomes embedded in deep-layer southwesterly flow ahead of the aforementioned trough. All of the global models agree on this general scenario, though there are differences regarding the exact timing that Oscar will begin its recurvature and how quickly it will accelerate across the northern Atlantic. That said, the track consensus aids have changed very little, and no significant changes were made to the previous track forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 25.5N 53.8W 60 KT 70 MPH 12H 29/0000Z 25.6N 55.8W 65 KT 75 MPH 24H 29/1200Z 26.2N 57.8W 65 KT 75 MPH 36H 30/0000Z 27.3N 58.4W 70 KT 80 MPH 48H 30/1200Z 29.3N 57.8W 75 KT 85 MPH 72H 31/1200Z 37.1N 51.3W 80 KT 90 MPH 96H 01/1200Z 45.5N 40.0W 65 KT 75 MPH 120H 02/1200Z 53.0N 22.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky
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Tropical Storm Oscar Forecast Discussion Number 6
2018-10-28 09:34:44| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Oct 28 2018 000 WTNT41 KNHC 280834 TCDAT1 Tropical Storm Oscar Discussion Number 6 NWS National Hurricane Center Miami FL AL162018 500 AM AST Sun Oct 28 2018 Deep convection near the center of Oscar has diminished somewhat over the past several hours. However, there are tightly curved cloud bands very near the center indicating a well-organized cyclone. Given that the central convection has not increased, the current intensity estimate is held at 55 kt which is a little above the latest subjective and objective Dvorak estimates but close to the value indicated by the previous scatterometer data. Oscar should remain in a moderate vertical shear environment, and over 26-27 deg C SSTs, for the next couple of days which would allow for some strengthening. The official forecast is close to the latest intensity model consensus and calls for the system to become a hurricane soon. Near or just beyond 96 hours, the shear is forecast to increase substantially and Oscar should begin to make the transition to an extratropical cyclone. The storm has been moving southwestward, or 235/13 kt, on the southeastern side of a northeast to southwest-oriented mid-level ridge. The ridge is likely to build to the north of Oscar within 12 to 24 hours, resulting in a turn toward the west. The cyclone should then turn toward the northwest and north as the ridge shifts eastward and a trough moves off the eastern U.S. coast. In the latter half of the forecast period, the system should accelerate north-northeastward to northeastward in the flow ahead of the trough. The official track forecast is close to the latest dynamical model consensus, and similar to the previous NHC track. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 25.0N 52.6W 55 KT 65 MPH 12H 28/1800Z 25.0N 54.5W 65 KT 75 MPH 24H 29/0600Z 25.5N 56.7W 70 KT 80 MPH 36H 29/1800Z 26.4N 58.0W 75 KT 85 MPH 48H 30/0600Z 27.9N 58.0W 75 KT 85 MPH 72H 31/0600Z 34.6N 53.6W 75 KT 85 MPH 96H 01/0600Z 42.5N 44.5W 60 KT 70 MPH 120H 02/0600Z 50.0N 28.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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Tropical Storm Oscar Forecast Discussion Number 5
2018-10-28 03:38:03| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Oct 27 2018 000 WTNT41 KNHC 280237 TCDAT1 Tropical Storm Oscar Discussion Number 5 NWS National Hurricane Center Miami FL AL162018 1100 PM AST Sat Oct 27 2018 Satellite imagery shows that convection associated with Oscar has become better organized, with increased banding around the low- level center. In addition, recent scatterometer data indicate that the system now has a relatively small wind field with a radius of maximum winds of about 25 n mi. Although the cyclone is still tangled up with the upper-level low to the point where it has not yet developed the anticyclonic outflow of a tropical cyclone, the convection and the wind field now justify calling the system a tropical storm. The initial intensity has been raised to 55 kt based on the scatterometer data, and it is possible this is a little conservative. The initial motion is a somewhat uncertain 240/17, as the short-term motion has been more toward the southwest or south. For the next several hours, Oscar should continue to pivot around the upper-level low to its east. Thereafter, it should turn more westward with a decrease in forward speed on the south side of a large ridge over the North Atlantic. After about 36 h, a large deep-layer trough moving eastward across the western Atlantic should cause Oscar to turn northwestward and northward, followed by recurvature into the westerlies and acceleration. The track guidance is generally in good agreement with this scenario, although by 120 h there is some spread in both the direction and forward speed after recurvature. The new forecast track is near the various consensus models, and the early part of it is shifted a little to the south of the previous forecast due to the current location and motion. The global models suggest that the core of Oscar should mostly avoid nearby strong upper-level winds through 24-36 h, and then encounter strong upper-level divergence associated with the deep-layer trough. While the environment is not ideal for a tropical cyclone, conditions appear favorable for additional intensification, and the intensity forecast now calls for Oscar to reach hurricane strength in about 24 h. Interaction with the trough after 72 h should start extratropical transition, which should be complete between 96-120 h. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 25.7N 51.4W 55 KT 65 MPH 12H 28/1200Z 25.2N 54.1W 60 KT 70 MPH 24H 29/0000Z 25.1N 56.5W 65 KT 75 MPH 36H 29/1200Z 25.8N 58.2W 70 KT 80 MPH 48H 30/0000Z 27.2N 58.6W 75 KT 85 MPH 72H 31/0000Z 32.5N 55.5W 75 KT 85 MPH 96H 01/0000Z 41.0N 47.0W 70 KT 80 MPH 120H 02/0000Z 48.5N 32.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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